1. Field of the Invention
The invention relates in general to powerline carrier communication systems, and more specifically to powerline carrier systems for performing distribution automation functions such as the automatic reading of utility meters, and selective load control.
2. Description of the Prior Art
The electrical utilities have used their transmission powerlines for many years for communication with remote switching and substation sites, for supervisory control purposes. The transmission lines are ideal for communication as they extend from the power generation site to the switching and substation sites without intervening obstacles to communication frequencies.
Communication over the distribution powerlines is much more difficult, and thus it is not a commonly used mode of communication for the electrical utilities. The distribution powerlines are susceptible to electrical noise and interference, and they have large numbers of distribution transformers, electrical loads, sectionalizing switches, capacitor banks, and the like, all of which provide some degree of attenuation for communication frequencies.
It is becoming increasingly more important to selectively and remotely control electrical loads, in order to reduce the magnitude of power demand peaks. Also, the availability of low cost non-volatile encoders due to the advances in large scale integration has made the automatic reading of utility meters attractive. Selective load control, automatic meter reading, and other distribution automation functions require some form of communication. Since the electrical utilities already have distribution powerlines which extend to each site to be communicated with, it would be desirable to use distribution powerline carrier for the communication mode, if the problems associated therewith can be economically dealt with.
U.S. Pat. Nos. 3,656,112; 3,702,460 and 3,815,119, all disclose some form of communication via the distribution network of an electrical utility. U.S. Pat. No. 3,656,112 discloses a communication system which uses a combination of electrical powerline and wireless. The wireless link is used to by pass distribution transformers and other obstructions located in the transmission path. U.S. Pat. No. 3,702,460 discloses making the neutral conductor of the distribution powerline available as a communication link by inserting a parallel resonant circuit between the neutral and ground, at each ground point in the system. The neutral-ground communication circuit bypasses distribution transformers. U.S. Pat. No. 3,815,119 uses the powerline conductor on the secondary side of a distribution transformer to transfer the various meter readings associated with the secondary to a common receiver point, where the readings are stored until they can be read, such as by a mobile unit which periodically travels near the receiver site and interrogates the site by a wireless link.
My co-pending application Ser. No. 425,759, filed Dec. 18, 1973, entitled "A Distribution Network Powerline Carrier Communication System", which is assigned to the same assignee as the present application, sets forth a new and improved arrangement for communicating over distribution powerlines. In this co-pending application, a substation area is divided into zones, and the zones, when interrogated by signals from an interrogation source, respond at different frequencies. Frequency changing or translating repeaters interface the zones to maintain zone isolation while boosting the strength of the signals within the zone. This multifrequency arrangement reduces the possibility of a response signal acting as an interrogation signal.
The present application is an improvement upon the communication system of my hereinbefore mentioned co-pending application, with the improvement allowing obstructions, such as distribution transformers, to be easily circumvented without direct metallic connection with the high voltage primary side of the transformer.